The term “intaglio printing” as used herein refers to direct plate printing using engraved printing plates as commonly used for the production of banknotes and security documents. Banknotes, for example, are typically provided with intaglio-printed patterns (such as portraits or other pictorial representations, latent images, guilloche patterns, denominations, bank designation, etc.) which are readily recognizable by touch due to the embossing and tactile effect inherent to intaglio printing.
Intaglio printing is to be distinguished from so-called gravure or rotogravure printing (or “Tiefdruck” in German) which makes use of engraved cylinders provides with arrays of cells of varying depth and/or width and is performed using low viscosity inks and low printing pressures. In contrast, intaglio printing is carried out using high viscosity, pasty inks and high printing pressures and produces a characterizing relief and embossing on the resulting printed products, which relief and embossing might be recognized by touch.
Sheet-fed intaglio printing presses are for instance known from European patent applications Nos. EP 0 091 709 A1, EP 0 406 157 A1, EP 0 563 007 A1, EP 0 873 866 A1, EP 1 602 482 A1 all in the name of the present Applicant. These printing presses are only adapted to carry out intaglio printing of one side of the sheets.
European patent applications Nos. EP 0 343 105 A2, EP 0 343 106 A2, EP 0 949 069 A1, all in the name of the present Applicant, disclose sheet-fed offset printing presses for simultaneous recto-verso printing of sheets for the production of banknotes and the like securities. These offset printing presses, also commonly referred to as Simultan-type presses, are used to print multicolour backgrounds on both sides of the sheets simultaneously and with precise recto-verso register.
European patent applications EP 0 132 857 A1 (which corresponds to BE 901 555), EP 0 136 972 A1 and EP 0 351 366 A2, all in the name of the present Applicant, disclose so-called combined printing presses for performing offset printing and intaglio printing of sheets for the production of banknotes and the like securities in one pass. Offset printing is performed on one or both sides of the sheets in an offset printing unit, which sheets are then fed to a downstream-located intaglio printing unit which prints the sheets on only one side.
German patent DE 1 561 068 B1 discloses a four-colour offset printing press for single-side or recto-verso printing of sheets, which printing press includes first and second printing units disposed in a mirrored configuration. Each printing unit comprises first and second blanket cylinders and associated forme cylinders inked by corresponding inking devices. The two printing units are each adapted to be configured to perform either single-side printing or recto-verso printing of the sheets. For single-side printing of the sheets, each printing unit is configured so that the first and second blanket cylinders cooperate with the same side of the sheets and the sheets are conveyed from the first to the second printing unit by means of a first chain conveyor system running below the printing units. For recto-verso printing of the sheets, each printing unit is configured so that the first and second blanket cylinders cooperate with opposite sides of the sheets and the sheets are conveyed from the first to the second printing unit by means of a second chain conveyor system running above the first chain conveyor system. Recto-verso printing is thus performed in a simultaneous manner in each printing unit.
British patent GB 393,992 A discloses a sheet conveying device for coupling of individual printing presses in tandem configuration. The sheet conveying device is coupled to the chain conveyor system of the first printing press, downstream of the sheet delivery station thereof. In order to perform recto-verso printing of the sheets, a sheet-turning device is further provided, which sheet-turning device is coupled to the chain conveyor system of the first printing press so that sheets can be deposited on the sheet conveying device with their printed side oriented downwards. The thus turned sheets are then fed by the sheet conveying device to the downstream located second printing press.
German patent DE 949 474 C (which corresponds to British patent GB 761,456 A) discloses a sheet-fed rotogravure printing press for multicolour printing consisting of several identical printing units disposed in tandem configuration and each provided with its own feed table and delivery chain conveyor system. The delivery chain conveyor system of each printing unit transfers the printed sheets to a secondary delivery chain system which is placed above the feed table of the subsequent printing unit where the sheets are deposited in an overlapping formation. The secondary delivery chain system can be selectively operated to perform reversal of the sheets before deposition thereof onto the underlying feed table so as to carry out recto-verso printing of the sheets. According to German patent DE 949 474 C, the sheets are dropped by the secondary delivery chain system in an overlapped manner on the subsequent feed table, which requires re-alignment and separation of each individual sheet before it can be fed to the subsequent printing unit.
German patent DE 958 385 C discloses a sheet-fed rotogravure printing press for multicolour printing which is only adapted to perform single-side printing of the sheets.
US patent application No. US 2005/0042072 A1 discloses a transportation system for sheet delivery between sheet or sheet stack processing equipment. A sheet or sheet stack processing module is configured to include one or more transfer stations for receiving either single sheets of stacks of sheets to be passed onto the processing module, each transfer station comprising a slotted platform around which a belt rotates to pass sheets deposited on the platform to the sheet or sheet stack processing module. The platform is slotted so as to have a plurality of alternating platform fingers and platform slots that may intermesh with the platform fingers and slots of another transfer station or of a moveable transportation cart having a slotted deck. In this way, the output of a first sheet or sheet stack processing module may be directly coupled to the input of a subsequent sheet or sheet stack processing module. This publication does not teach any sort of automated guided vehicle system for transferring sheets between two remote locations. The transportation system of US 2005/0042072 A1 is suitable for use in the context of office printing equipment such as photocopiers or digital printers. This solution is however not adapted in the context of industrial sheet-fed printing presses, such as used for the production of securities, due in particular to the configuration of sheet feeders and sheet deliveries of sheet-fed printing presses. It is in particular not possible to directly couple the sheet delivery of a sheet-fed printing press to the sheet feeder of another printing press using a system as taught in US 2005/0042072 A1.
Simultaneous recto-verso printing as taught in EP 0 132 857 A1. EP 0 343 105 A2, EP 0 343 106 A2, EP 0 351 366 A2, EP 0 949 069 A1 or DE 1 561 068 B1 is not applicable in practice to intaglio printing which requires a compromise between a hard surface on the printing side (i.e. where the plate cylinder and intaglio printing plate(s) are located) to ensure precise printing and an elastic surface on the opposite side (i.e. where the impression cylinder is located) to ensure that the sheets are properly pressed against the hard surface of the intaglio printing plate(s) and into the engravings thereof to catch the ink contained therein. A solution for simultaneous recto-verso printing was proposed in Swiss patent No. CH 414 686 A5 in the name of the present Applicant, but this solution has never been put successfully into practice because of the above-mentioned necessary compromise.
Security against forgery is improved by providing intaglio patterns on both sides of the printed sheets. This is typically performed in two separate intaglio printing presses each equipped with a corresponding set of intaglio printing plates for the back side and the front side of the sheets. Sheets processed by the first printing press are transported manually to the sheet feeding station of the second printing press.